Which of the following expressions is not equivalent to sin2(x)?

Question

Which of the following expressions is not equivalent to sin²(x)?

1. 1+cos²(x)
2. tan²(x)cos²(x)
3. sin²(x) / sin²(x) + cos(x)
4. sin⁴(x) / cos²(x) tan²(x)

Answer 1

Much of this is based off the fundamental rule that cos²x + sin²x = 1. This derives from the definitions of sin and cosine and the fact that the sum of squares of the x and y coordinates of a unit-circle centered on the origin is 1, i.e., the radius.

You'll also need to know that tanx = sinx / cosx

Put these two facts together and you should be able to figure out which expressions are not equal to sin²x