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Math Challenge 3 Chapter 4
4.3 A: I don't understand how they go from the 1st to the second step. I get how they do (a^2+b^2) = (a-b)(a+b)
B: I dont get how they go from 2sin140 --> 2sin40
** Is there a 1/3 angle identity. I know there's a triple angle one. If there is, that would very helpful since then I wouldn't have trouble doing the first few problems. If there is, please give a proof so I can understand it. I'm mostly having trouble with sin/tan/cos of 20.**
4.14: How are we supposed to figure out the cos of 18?
Hint for Part A: Factor and then use Pythagorean Identity and a double angle identity.
Hint for Part B: $70 degrees is 90 degrees - 20 degrees. Combine into a fraction and apply double angle formulas to convert between 20 degrees and 40 degrees.
Update: I was able to figure out problem 4.14. Hint: Don't try to evaluate each one individually. Try multiplying and dividing the expression by something to "complete the double angle formula." That could work because each term in the product has an angle that is twice the angle in the previous term.
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