Answers

2015-10-18T09:59:23+05:30
In a right angled triangle ABC, cosA = 2/5.
See the attachment.
cosA = AB/AC = 2/5
let BC = x

Using Pythagoras theorem
x² + 2² = 5²
⇒ x² + 4 = 25
⇒ x² = 25-4 = 21
⇒ x = √21

sin A = BC/AC = √21/5

2. tanA is a positive zero of x² - 1 = 0
x² - 1 = 0
⇒ x² = 1
⇒ x = +1 or -1
Since tanA is the positive zero of x²-1=0;
tanA = 1
⇒ A = 45° 
1 5 1