Find the slope of the tangent to the curve at the point where . Find the angle which this tangent makes with the curve , where . Submit your answer as the angle in degrees. You may use the fact that .
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The slope of the tangent to y = 2 x 1 + 3 at x = − 1 is d x d y ∣ ∣ ∣ ∣ x = − 1 = − 2 x 2 1 ∣ ∣ ∣ ∣ x = − 1 = − 2 1 .
Then y ( − 1 ) = 2 ( − 1 ) 1 + 3 = 2 5 and the equation of the tangent is x + 1 y − 2 5 = − 2 1 , ⟹ y = 2 − 2 x .
When the tangent meet the other curve y = 2 x 2 + 2 :
2 − 2 x 2 x 2 + 2 x 4 x 2 + x x ( 4 x + 1 ) = 0 ⟹ x = 2 x 2 + 2 = 0 = 0 = − 4 1 Since x < 0
The slope of the curve y = 2 x 2 + 2 at x = − 4 1 is d x d y ∣ ∣ ∣ ∣ x = − 4 1 = 4 x ∣ ∣ ∣ ∣ x = − 4 1 = − 1 .
The angle between the tangent and the curve is tan − 1 1 − tan − 1 2 1 ≈ 4 5 ∘ − 2 6 ∘ = 1 9 ∘