Question

why is value of sin 90 =1

Answer 1

Look at point (0, 1) on unit circle.

Answer 2

sin(90)=1
this says that the side opposite of the 90 and the hypotenuse are the same length. This is because the side opposite the 90 degree angle is the hypotenuse. So they are the same length, and when in a ratio, a/a = 1.

so, we know only that the hypotenuse is some length, we can't know what the actual length is unless we are given one side, because a trig function only gives ratios.

the sides could be any value (or multiple of value) of a^2+b^2=1
Depending on the values of a, and b, the other two angles will vary.

As you can see, w/o more information, like the actual length of some sides on the triangle, we can't be sure of much

Answer 3

It is by definition of the sine using the "unit circle"
See http://www.khanacademy.org/math/trigonometry/basic-trigonometry/unit_circle_tut/v/unit-circle-definition-of-trig-functions-1

Answer 4

thanks all.....

Answer 5

np:)