tan(θ - φ) = (tanθ - tanφ)/(1 + tanθ*tanφ)
I hope this is in the right place.
Prove the following statement by a direct proof of the contrapositive statement.
If two lines are perpendicular, the product of their gradients is -1.
The contrapositive would be:
If the products of two gradients is not -1, then their lines are not perpendicular.
My problem is I don't know how to go about proving the statement.
I tried this:
is not equal to 2
But I don't know how to continue.