Text description - screencast for exercise 7

[The narrator reads out the onscreen text.]

NARRATOR: Exercise 7. Prove that 1 divided by sec theta plus tan theta is equal to cos theta divided by 1 plus sin theta. We begin with the left-hand side, 1 divided by sec theta plus tan theta, and write this out as a division so that we can express sec theta and tan theta as fractions. So we have 1 divided by 1 over cos theta plus sin theta over cos theta. So that is 1 divided by 1 plus sin theta all divided by cos theta, which is equivalent to 1 multiplied by cos theta divided by 1 plus sin theta, which equals cos theta divided by 1 plus sin theta, which is equal to the right-hand side, and so we have proven that 1 divided by sec theta plus tan theta equals cos theta divided by 1 plus sin theta as was required.