Question

Find the value of cos 2 alpha when sin alpha =9/10​

Answer 1

Find the value of cos 2α when sinα =9/10​

cos2α=1-2sin²α(use this formula below)

solution;

cos2α

1-2sin²α

1-2(9/10)²

1-2(81/100)

1-(81/50)

50-81/50

-31/50