Question

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Answer 1

soln refers to the attachment

Answer 2

Note:

sin(A+B) = sinA•cosB + cosA•sinB

sin(A-B) = sinA•cosB - cosA•sinB

cos(A+B) = cosA•cosB - sinA•sinB

cos(A-B) = cosA•cosB + sinA•sinB

Sometimes it is easier to get the expression for dy/dx ,by differentiating the expression with respect to y and then applying Invertendo.

(reciprocal both sides).

Invertendo rule;

If a/b = c/d

Then, b/a = d/c

For explaination, please refer to the attachment.