In triangle ABC, angle C = 90 degrees sinA = 7/5 find cosA.
| June 1, 2021 | education
In a triangle abc, the angle is c = 90 °.
It is known that sin A = 7/5.
Find cos A.
We apply the basic trigonometric identity.
sin ^ 2 a + cos ^ 2 a = 1;
(7/15) ^ 2 + cos ^ 2 a = 1;
cos ^ 2 a = 1 – (7/15) ^ 2;
cos ^ 2 a = 1 – 49/225;
cos ^ 2 a = 225/225 – 49/225;
cos ^ 2 a = 176/225;
cos a = √ (176/225);
cos a = √176 / 15;
cos a = 4/15 * √11.
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