Properties of Triangles MCQ Quiz in मल्याळम - Objective Question with Answer for Properties of Triangles - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക
Last updated on Mar 8, 2025
Latest Properties of Triangles MCQ Objective Questions
Top Properties of Triangles MCQ Objective Questions
Properties of Triangles Question 1:
In a triangle ABC, sin A - cos B - cos C = 0. What is angle B equal to?
Answer (Detailed Solution Below)
Properties of Triangles Question 1 Detailed Solution
Formula used :
sin 2θ = 2 sin θ cos θ
cos C + cos D = 2cos(\(\frac{C+D}{2}\)) cos(\(\frac{C-D}{2}\))
Calculaton :
sin A - cos B - cos C = 0
⇒ sin A = cos B + cos C
Using the formula given above
⇒ 2 sin(A/2) cos(A/2) = 2cos(\(\frac{B+C}{2}\)) cos(\(\frac{B-C}{2}\))
We know that, for a ΔABC, ∠ A + ∠ B + ∠ C = π
⇒ sin(A/2) cos(A/2) = cos(\(\frac{π - A}{2}\)) cos(\(\frac{B-C}{2}\))
Since, cos(π/2 - θ) = sin θ
⇒ sin(A/2) cos(A/2) = sin(\(\frac{ A}{2}\)) cos(\(\frac{B-C}{2}\))
⇒ cos(A/2) = cos(\(\frac{B-C}{2}\))
⇒ A/2 = (B - C)/2
⇒ A = B - C
⇒ B = A + C
But ∠ A + ∠ B + ∠ C = π
⇒ B = π - B
⇒ 2B = π
⇒ B = π/2
∴ Angle B is equal to \(\frac{\pi}{2}\).
Properties of Triangles Question 2:
If a, b, c are the sides of a triangle ABC, then \({a^{\frac{1}{p}}} + {b^{\frac{1}{p}}} - {c^{\frac{1}{p}}}\) where p > 1, is
Answer (Detailed Solution Below)
Properties of Triangles Question 2 Detailed Solution
Concept:
- The triangle inequality states that for any triangle, the sum of the lengths of any two sides must be greater than or equal to the length of the remaining side.
Calculation:
Given: a, b, c are the sides of a triangle ABC
Since, a, b, c are positive numbers.
⇒ a1/p, b1/p, c1/p are positive numbers. ...(∵ p > 1)
We know that sum of any two sides must be greater than third side.
⇒ a1/p + b1/p > c1/p
⇒ a1/p + b1/p - c1/p > 0
∴ Option 2 is correct.Properties of Triangles Question 3:
In a triangle ABC, ∠A = y, ∠B = x and ∠C = y + 20. If 2x – y = 20, then the triangles is:
Answer (Detailed Solution Below)
Properties of Triangles Question 3 Detailed Solution
Concept:
Angle sum property: The sum of the angles of a triangle is 180°.
Types of triangles:
- Acute angle triangle: If all the angles of a triangle are less than 90° then it is an acute angle triangle
- Obtuse angle triangle: If any one of the angles of a triangle is greater than 90° then it is an obtuse angle triangle.
- Right angle triangle: If one angle of a triangle is 90° and the side opposite to 90° is the longest side then it is a right angle triangle.
- Equilateral Triangle: If all the angles of a triangle are 60° then it is an equilateral triangle.
Calculation:
Given: In Δ ABC ∠A = y, ∠B = x and ∠C = y + 20 and 2x – y = 20.
As we know that sum of all the angles of triangle = 180°
y + x + y + 20 = 180
x + 2y = 160 ----(1)
2x – y = 20 ----(2)
From (1) and (2)
x = 40° and y = 60°
The angles are 40°, 60° and 80°
As we can see that all angles of Δ ABC are less than 90°
∴ Δ ABC is an acute angled triangleProperties of Triangles Question 4:
In a triangle ABC. if b = 2, c = 3 and ∠B = \(\frac{\pi }{6}\) then 'a' satisfies the equation
Answer (Detailed Solution Below)
Properties of Triangles Question 4 Detailed Solution
Concept:
Cosine Rule:
a2 = b2 + c2 - 2bc cosA
b2 = a2 + c2 - 2ac cosB
c2 = b2 + a2 - 2ab cosC
The formula can be rearranged to:
\(cosA=\frac{b^{2}+c^{2}-a^{2}}{2bc}\)
\(cosB=\frac{a^{2}+c^{2}-b^{2}}{2ac}\)
\(cosC=\frac{a^{2}+b^{2}-c^{2}}{2ab}\)
Solution:
Given, In a triangle ABC
b = 2, c = 3 and ∠B = \(\frac{\pi }{6}\)
By using Cosine Rule in ΔABC,
\(cosB=\frac{a^{2}+c^{2}-b^{2}}{2ac}\)
⇒ \(cos\frac{\pi }{6}=\frac{a^{2}+3^{2}-2^{2}}{2.a.3} \)
⇒ \(\frac{\sqrt{3}}{2}=\frac{a^{2}+5}{6a} \)
⇒ \(a^{2}-3\sqrt{3}a+5=0\)
∴ The correct option is (3)
Properties of Triangles Question 5:
In ΔABC, ∠C = 54°, the perpendicular bisector of AB at D meets BC at E. If ∠EAC = 42°, then what is the value (in degrees) of ∠ABC?
Answer (Detailed Solution Below)
Properties of Triangles Question 5 Detailed Solution
∠C = 54° and ∠EAC = 42°, So ∠AEC = 84° (sum of all angles of triangle = 180°)
∴ ∠BEA = 180 - 84 = 96°.
∵ DE bisects AB perpendicularly, so angle made by BD and DA should be equal.
∴ ∠DBE + ∠BED + ∠EDB = 180°
∴ ∠DBE + 96/2 + 90 = 180
∴ ∠ABC = ∠DBE = 180 - 90 - 48 = 42°
Properties of Triangles Question 6:
In a triangle ABC, a – 2b + c = 0. The value of \(\cot \left( {\frac{A}{2}} \right)\cot \left( {\frac{C}{2}} \right)\) is
Answer (Detailed Solution Below)
Properties of Triangles Question 6 Detailed Solution
CONCEPT:
Properties of Triangles:
If three sides a, b and c are sides of a triangle, \({\rm{\Delta }} = {\rm{\;}}\sqrt {{\rm{s}}\left( {{\rm{s}} - {\rm{a}}} \right)\left( {{\rm{s}} - {\rm{b}}} \right)\left( {{\rm{s}} - {\rm{c}}} \right)} \)where \({\rm{s}} = \frac{{{\rm{a}} + {\rm{b}} + {\rm{c}}}}{2}\) where
S = semi perimeter of a triangle
Half angle formulae of a triangle:
In Δ ABC
- \(\sin \left( {\frac{{\rm{A}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{({\rm{s}} - {\rm{b}}(\left( {{\rm{s}} - {\rm{c}}} \right)}}{{{\rm{bc}}}}} \)
- \(\cos \left( {\frac{{\rm{A}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{{\rm{s}}\left( {{\rm{s}} - {\rm{a}}} \right)}}{{{\rm{bc}}}}} \)
- \(\tan \left( {\frac{{\rm{A}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{\left( {{\rm{s}} - {\rm{b}}} \right)\left( {{\rm{s}} - {\rm{c}}} \right)}}{{{\rm{s}}\left( {{\rm{s}} - {\rm{a}}} \right)}}} \)
CALCULATION:
Given that, a – 2b + c = 0
⇒ a + c = 2b
As we know that, S (Semi perimeter) of a triangle = (a + b + c)/2
⇒ s = (2b + b) /2 = 3b/2
As we know that, \({\rm{Cot\;}}\left( {\frac{{\rm{A}}}{2}} \right) = \sqrt {\frac{{{\rm{s}}\left( {{\rm{s}} - {\rm{a\;}}} \right)}}{{\left( {{\rm{s}} - {\rm{b}}} \right)\left( {{\rm{s}} - {\rm{c}}} \right)}}} ,\cot \left( {\frac{{\rm{c}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{{\rm{s}}\left( {{\rm{s}} - {\rm{c}}} \right)}}{{\left( {{\rm{s}} - {\rm{a}}} \right)\left( {{\rm{s}} - {\rm{b}}} \right)}}} \)
\(\Rightarrow \cot \left( {\frac{{\rm{A}}}{2}} \right)\cot \left( {\frac{{\rm{c}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{{\rm{s}}\left( {{\rm{s}} - {\rm{a\;}}} \right)}}{{\left( {{\rm{s}} - {\rm{b}}} \right)\left( {{\rm{s}} - {\rm{c}}} \right)}}} \sqrt {\frac{{{\rm{s}}\left( {{\rm{s}} - {\rm{c}}} \right)}}{{\left( {{\rm{s}} - {\rm{a}}} \right)\left( {{\rm{s}} - {\rm{b}}} \right)}}} \)
\(\Rightarrow \cot \left( {\frac{{\rm{A}}}{2}} \right)\cot \left( {\frac{{\rm{c}}}{2}} \right) = {\rm{\;}}\sqrt {\frac{{{{\rm{s}}^2}}}{{{{\left( {{\rm{s}} - {\rm{b}}} \right)}^2}}}} \)
\(\Rightarrow \cot \left( {\frac{{\rm{A}}}{2}} \right)\cot \left( {\frac{{\rm{c}}}{2}} \right) = \frac{{\rm{s}}}{{\left( {{\rm{s}} - {\rm{b}}} \right)}}\)
\(\Rightarrow \cot \left( {\frac{{\rm{A}}}{2}} \right)\cot \left( {\frac{{\rm{c}}}{2}} \right) = \frac{{\frac{{3{\rm{b}}}}{2}}}{{\frac{{3{\rm{b}}}}{2} - {\rm{b}}}} = 3\)Properties of Triangles Question 7:
If the angles of a triangle ABC are in AP and b : c = √3 : √2, then find the value of sin (B + C)?
Answer (Detailed Solution Below)
Properties of Triangles Question 7 Detailed Solution
Concept:
If A, B and C are angles and a, b and c are the sides of a ΔABC, then: \(\frac{a}{\sin A}=\frac{b}{\sin B}=\frac{c}{\sin C~}\)
sin (x + y) = sin x ⋅ cos y + sin y ⋅ sin x
Calculation:
Let us consider Δ ABC with A, B and C as its angles and a, b and c as its sides.
Given: Angles are in AP i.e A, B and C are in AP.
⇒ 2 × B = A + C
As we know that, A + B + C =180°
⇒ 3 × B = 180° ----(∵ 2 × B = A + C)
⇒ B = 60°
As we know that, if A, B and C are angles and a, b and c are the sides of a Δ ABC, then:
\(\frac{a}{\sin A}=\frac{b}{\sin B}=\frac{c}{\sin C~}\)
\(⇒ \frac{b}{c}=\frac{\sin B}{\sin C}\)
As it is given that b : c = √3 : √2 and sin C = sin 60° = √ 3 / 2.
\(⇒ \frac{√{3}}{√{2}}=\frac{\frac{√{3}}{2}}{\sin C}~⇒ \sin C=\frac{1}{√{2}}\)
⇒ C = 45°
As we know that, sin (x + y) = sin x ⋅ cos y + sin y ⋅ sin x
⇒ sin (B + C) = sin B ⋅ cos C + sin C ⋅ cos B
⇒ sin (B + C) = √3 / 2 ⋅ 1 / √2 + 1 / √2 ⋅ 1 / 2 = 1 + √3 / 2√2
Properties of Triangles Question 8:
In ΔABC, ∠B = 90°, AC = 169 cm, and BC = 120 cm. The length of AB (in cm) is
Answer (Detailed Solution Below)
Properties of Triangles Question 8 Detailed Solution
Given:
In ΔABC, ∠B = 90°, AC = 169 cm, and BC = 120 cm
Concept used:
ABC is a right angled triangle at B
Pythagoras theorem = AC2 = AB2 + BC2
Calculation:
BC = 120 cm, AC = 169 cm
According to Pythagoras theorem,
⇒ (169)2 = AB2 + (120)2
⇒ AB2 = 14161
⇒ AB = 119 cm
∴ Option 3 is correct.
Properties of Triangles Question 9:
Consider the following statements:
1. If ABC is a right-angled triangle, right-angled at A, and if sin \(\rm B = \frac 1 3,\) then cosec C = 3.
2. If b cos B = c cos C and if the triangle ABC is not right-angled, then ABC must be isosceles.
Which of the above statements is/are correct?
Answer (Detailed Solution Below)
Properties of Triangles Question 9 Detailed Solution
Concept:
Pythagoras theorem: In a right-angled triangle, the square of the hypotenuse side is equal to the sum of squares of the other two sides.
Sine Rule in triangle ABC, having sides a, b, c:
\(\rm \frac{\sin A}{a}=\frac{\sin B}{b}=\frac{\sin C}{c}=\frac{1}{K}\)
sin A - cos B = \(\rm 2\cos(\frac{A +B}{2})\sin(\frac{A -B}{2})\)
Calculation:
1. We have,
sin \(\rm B = \frac 1 3=\frac{P}{H}\)
Hwence, Right angle triangle can be drawn as,
Here, P = 1
H = 3
B = x
Using Pythagoras theorem,
32 = 12 + x2
x2 = 8
\(\therefore x=2\sqrt{2}\)
Now , Cosec C = \(\frac{3}{2\sqrt{2}}\)
Hence Ststement (1) is not correct.
2. Given,
b cos B = c cos C
Using the sine rule,
\(\rm \frac{\sin A}{a}=\frac{\sin B}{b}=\frac{\sin C}{c}=\frac{1}{K}\)
⇒ b = K sin B & c = K sin C
⇒ 2 sin B cos B = 2 sin C cos C
Assume,
K = 2
⇒ 2 sin B cos B = 2 sin C cos C
⇒ sin 2B = sin 2C [2 sin x cos x = sin 2x]
⇒ sin 2B - sin 2C = 0
Using Formula:
sin C - sin D = 2 cos \((\frac{C+D}{2})\) × sin \((\frac{C-D}{2})\)
⇒ 2 cos (B + C) sin (B - C) = 0
In this case,
Either,
cos (B + C) = 0
Hence, (B + C) = 90° .... (1)
Or,
Or sin (B -C) = 0
B - C = 0
⇒ B = C .... (2)
From equation (1) & (2),
B = C = 45°
So ABC must be issosceles
Hence, option (2) is correct.
Properties of Triangles Question 10:
In a triangle ABC if the angles A, B, C are in AP, then which one of the following is correct?
Answer (Detailed Solution Below)
Properties of Triangles Question 10 Detailed Solution
Concept:
The sum of the angles of the triangle is 180º.
Cosine formula: cos(B) = \(\rm \dfrac{a^2+c^2-b^2}{2ac}\)
Calculations:
Given, in a triangle ABC if the angles A, B, C are in AP.
⇒2B = A+ C
We know that, the sum of the angles of the triangle is 180º.
⇒ A + B + C = 180º
⇒ 2B + B = 180º
⇒ 3B = 180º
⇒B = 60º
By cosine formula, we have
cos(B) = \(\rm \dfrac{a^2+c^2-b^2}{2ac}\)
⇒cos(60º) = \(\rm \dfrac{a^2+c^2-b^2}{2ac}\)
⇒\(\rm\dfrac{1}{2}\) = \(\rm \dfrac{a^2+c^2-b^2}{2ac}\)
⇒\(\rm a^2+c^2-b^2= ac\)
⇒b2 = a2 + c2 - ac
Hence, In a triangle ABC if the angles A, B, C are in AP, b2 = a2 + c2 - ac is the correct statement.