Dorson's answer to :-)'s Secondary 3 A Maths Singapore question.
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1. Expand the expression
2. After expanding:
sin(75)² - 2sin(75)cos(75) + cos(75)²
Note that:
sin(A)² + cos(A)² = 1
sin(2A) = 2sin(A)cos(A)
3. Simplify
sin(75)² + cos(75)² =1
2sin(75)cos(75) = sin(150)
Simplifying: 1- sin (150) = 1- sin(30)
Recall: sin(30)=1/2
Hence the ans is: 1-1/2=1/2
2. After expanding:
sin(75)² - 2sin(75)cos(75) + cos(75)²
Note that:
sin(A)² + cos(A)² = 1
sin(2A) = 2sin(A)cos(A)
3. Simplify
sin(75)² + cos(75)² =1
2sin(75)cos(75) = sin(150)
Simplifying: 1- sin (150) = 1- sin(30)
Recall: sin(30)=1/2
Hence the ans is: 1-1/2=1/2
Date Posted:
3 years ago
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