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# In a ∆ABC, if

Question:

In a ∆ABC, if c2 + a2 – b2 = ac, then the measure of angle B is ____________.

Solution:

In a ∆ABC,

if c2 + a2 − bac

Since $\cos B=\frac{c^{2}+a^{2}-b^{2}}{2 a c}$

$=\frac{a c}{2 a c}$

i.e $\cos B=\frac{1}{2}$

i.e $B=\frac{\pi}{3}$