Question
Question: In ∆ABC (a + b)(a – b) = c(b + c), the measure of angle A, is-...
In ∆ABC (a + b)(a – b) = c(b + c), the measure of angle A, is-
A
300
B
600
C
900
D
1200
Answer
1200
Explanation
Solution
Assume that side 'a' is opposite to ∠A
Given, (a + b)(a – b) = c(b + c)
⇒ a2 – b2 = c2 + bc
a2 = b2 + c2 + bc = b2 + c2 – 2bc cosA (By law of cosines)
bc = –2bc cosA
cosA = –1/2 or ∠A = 1200