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secondary 4 | E Maths
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Kathy
Kathy

secondary 4 chevron_right E Maths chevron_right Singapore

How to do the working

Date Posted: 4 years ago
Views: 351
Eric Nicholas K
Eric Nicholas K
4 years ago
Later
Eric Nicholas K
Eric Nicholas K
4 years ago
8 sin^2 x + 2 cos^2 x
= 6 sin^2 x + 2 sin^2 x + 2 cos^2 x
= 6 sin^2 x + 2 (sin^2 x + cos^2 x)
= 6 sin^2 x + 2
= 6 * 0.5 * (1 - cos 2x) + 2 (using a rearranged double angle formula for cos 2x)
= 3 - 3 cos 2x + 2
= 5 - 3 cos 2x

Amplitude is 3 (not -3) and period 360 deg / 2 = 180 deg (or 2pi/2 = pi if the question is in radian mode).

Maximum is 8 when cos 2x equals -1 and minimum is 2 when cos 2x equals 1.

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Eric Nicholas K
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This is also possible, amongst several methods.
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syjiaxuan
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290 answers (A Helpful Person)
Hope this helps, impt parts in pink