OpenStax, Algebra and Trigonometry 2e §9.2 Sum and Difference Identities · Exercise 20 · Trigonometry · Compound & multiple angles

Sum and Difference Identities · Exercise 20

Find the requested information.

Given that $s ina = \frac{2}{3}$ and $cos b = - \frac{1}{4},$ with $a$ and $b$ both in the interval $[\frac{π}{2}, π),$ find $s in (a + b)$ and $cos (a - b) .$

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OpenStax, Algebra and Trigonometry 2e · §9.2 Sum and Difference Identities · Exercise 20

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