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One Angle of a Triangle is 60°. the Other Two Angles Are in the Ratio of 5: 7. Find the Two Angles. - Mathematics

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Question

One angle of a triangle is 60°. The other two angles are in the ratio of 5: 7. Find the two angles.

Sum

Solution

In Δ ABC,

Let ∠A = 60° and then ∠B: ∠C = 5: 7
But ∠A + ∠B + ∠C = 180° ........(Angles of a triangle)

⇒ 60° + ∠B + ∠C = 180°

⇒ ∠B + ∠C = 180°− 60° = 120°

Let ∠B = 5x and ∠C = 7x

∴ 5x + 7x = 120°

⇒ 12x = 120°

⇒ x =`(120°)/12=10°`

∴ ∠B = 5x = 5 × 10° = 50°

∠C = 7x = 7 × 10° = 70°

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Chapter 15: Triangles - Exercise 15 (A)

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Selina Concise Mathematics [English] Class 7 ICSE
Chapter 15 Triangles
Exercise 15 (A) | Q 10
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