Verify the identity: cos4u = cos^2 (2u) - sin^2 (2u)

The average human heart beats 72 beats per minute. how many times does it beat in 15 seconds?

Write the expression as a constant , a single trigonometric function, or a power of a trigonometric function. sin x cos x/ tan x

Solve with work both bert and ernie received an increase in their weekly salaries. bert's salary increased from $520 to $520. ernie's salary went from $580 to $645. find the percent of increase for each salary. what was the larger of the two percents ?