# C3 TrigWatch

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#1
www.jonathanb.co.uk/cds/?q=C_3_7_D_11

In the second part why can't you do this

1-4cos(2∅) + 3sin(2∅)

Maximum value is 8 when cos(2∅)=-1 and sin(2∅)=1, giving 1+4+3=8.

Minimum value is -6 when cos(2∅)1 and sin(2∅)=-1, giving 1-4-3=-6

Why is this wrong?

THANKS
0
5 years ago
#2
(Original post by krisshP)
Maximum value is 8 when cos(2∅)=-1 and sin(2∅)=1, giving 1+4+3=8.

Minimum value is -6 when cos(2∅)1 and sin(2∅)=-1, giving 1-4-3=-6

Why is this wrong?

THANKS
If cos(2∅)=-1 how could sin(2∅)=1 ??

Do you see?

when cos of some angle is -1, that angle must be so the sin would be zero (not 1)
0
#3
(Original post by Plato's Trousers)
If cos(2∅)=-1 how could sin(2∅)=1 ??

Do you see?

when cos of some angle is -1, that angle must be so the sin would be zero (not 1)
Yeah, that makes perfect sense, that's why it's better to put it in the R alpha form where you only have one trig function, sin in this case.

THANKS
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