# In the ABC triangle, the angle c is 90.cosA = √51 / 10. find sinA.

July 23, 2021 | education

| triangle ABC, ∡ c – straight line.

cos a = √51 / 10;

Find sin a.

Let’s write down the basic trigonometric identity.

sin ^ 2 a + cos ^ 2 a = 1;

Let us express sin a /

sin ^ 2 a = 1 – cos ^ 2 a;

sin ^ 2 a = 1 – (√51 / 10) ^ 2 = 1 – 51/100 = 100/100 – 51/100 = (100 – 51) / 100 = 49/100;

sin ^ 2 a = 49/100;

sin a = √ (49/100);

sin a = √ (7/10) ^ 2;

sin a = 7/10;

sin a = 0.7.

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