equations of tangent lines to curves

Question

Find equations of the tangent lines to the curve

y = (x − 1)/(x+1)

that are parallel to the line x − 2y = 4.

Y intercepts?

Answer 1

The tangents must have slope 1/2.

That means the derivative of the rational fraction must be equal to 1/2.

Remember the mnemonic downsie d upsie - upsie d downsie / downsie squared!