9. If five times a number plus two is 17, what is the number? A. 5 B. 2 C. 3 D. 7
2 answers:
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Answer:
1 + cosa sina
Step-by-step explanation:
cos³a - sin³a ← is a difference of cubes and factors in general as
a³ - b³ = (a - b)(a² + ab + b²) , then
cos³a - sin³a
= (cosa - sina )(cos²a + cosa sina + sin²a)
= (cosa - sina)(1 + cosa sina) [ sin²a + cos²a = 1 ]
Then
= ← cancel (cosa - sina) on numerator/ denominator
= 1 + cosa sina