Question

If the a=6,b=5,c=9,then the value of angle A is

Answer 1

Step-by-step explanation:

using cosine formula

$\cos(a) =( {b}^{2} + {c}^{2} - {a}^{2} ) \div 2bc$

substitute and get the answer

hope this will help u

Answer 2

Step-by-step explanation:

Given that,

• a = 6, b = 5 and c = 9

To find:

• ∠A (Angle A)

To find the angle, we must know the simple formula to find an angle of a triangle where the value of the sides are given,

The formula is as follow-

$a^{2}$ = $b^{2}$ + $c^{2}$ - 2cos(a)

∴ cos(a) = $\frac{b^{2}+ c^{2} - a^{2} }{2bc}$

cos(a) = $\frac{5^{2}+ 9^{2}- 6^{2} }{2*5*9}$

∴ cos(a) = $\frac{25 + 81 - 36}{90}$

cos(a) = $\frac{70}{90}$

∠A = $cos^{-}$($\frac{7}{9}$)

∴ ∠A = 38.94° ≅ 40°