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secondary 3 | A Maths
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ann
Ann

secondary 3 chevron_right A Maths chevron_right Singapore

need help with part b. think there’s something wrong when i use R formula. thank you

Date Posted: 2 years ago
Views: 366
sstrike
Sstrike
2 years ago
(b)
square at both sides

- 2 ∙ cos(x) ∙ sin(x) + cos²x + sin²x = 2
cos(x) ∙ sin(x) = -½

square at both sides
cos²x ∙ sin²x = ¼

(1 - sin²x) ∙ sin²x = ¼

sin²x = a
(1 - a) ∙ a = ¼

4a² - 4a + 1 = 0
(2a-1)² = 0
a = ½ = sin²x

sin(x) = ±√½

x₁ = 45°  ✗✗
x₂ = 315° ✓✓

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sstrike
Sstrike's answer
5576 answers (A Helpful Person)
1st
Try
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Arnold K H Tan
Arnold K H Tan's answer
2155 answers (A Helpful Person)
Using R-formula. Its my preference to use sine, for R formula.