In the ABC triangle, the angle c is 90, cosB = 3√11 / 10, find cosA?

In the ABC triangle, the angle c is 90, cos B = 3 * √11 / 10.

Find cos A.

Decision.

It is known that cos a = sin b = ac / ab;

Find sin b by the formula sin b = √ (1 – cos ^ 2 b);

sin b = √ (1 – (3√11 / 10) ^ 2) = √ (1 – 9 * 11/100) = √ (100/100 – 99/100) = √1 / 100 = 1/10 = 0.1 ;

Hence, cos a = sin b = 0.1.

As a result, we got that cos a = 0.1.