Posted by **Sara** on Tuesday, October 18, 2011 at 12:03am.

The graph of sinx and cosx intersect once between 0 and pi/2. What is the angle between the two curves at the point where they intersect? (You need to think about how the angle between two curves should be defined).

- CALCULUS ONE! -
**Reiny**, Tuesday, October 18, 2011 at 12:10am
first find their intersection

sinx = cosx

sinx/cosx = 1

tanx = 1

x = 45° or π/4 radians

for y = sinx , dy/dx = cosx

so at x = π/4 , dy/dx = 1/√2

tan^-1(1/√2) = 35.26°

for y = cosx , dy/dx = -sinx

so at x = π/4 , dy/dx = -1/√2

tan^-1(-1/√2) = 144.74°

angle between the two tangents = 144.74 - 35.26 = 109.48°

set your calculator to radians if you need your answer in radians.

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