O-Level Additional Math

[lotto]

dazzlego:

lotto:

[quote=\"red rose\"]Hi! Would appreciate help with 2 Trig Qs. Solve:


1. cot(2y+10°)=-0.5

2. 2 sin y + 1 = 3/cosec^2 y

Thanks!

Second question is abit complicated. Please check my work if there is any mistakes.
2 sin y + 1 = 3 sin^2 2y
2 sin y + 1 = 3 sin 2y sin 2y
2 sin y + 1 = 3 (2 sin y cos y) (2 sin y cos y)
2 sin y + 1 = 12 sin^2 y cos^2 y
2 sin y + 1 = 12 sin^2 y (1 - sin^2 y)
2 sin y + 1 = 12 sin^2 y - 12 sin^4 y
12 sin^4 y - 12 sin^2 y + 2 sin y + 1 = 0
Let x= sin y
12 x^4 - 12 x^2 + 2 x + 1 = 0
U can factorize it and get 4 value of x which will lead u to 4 value of y.
I am not sure about it. There must be wrong somewhere. Or maybe we need to try another substitution.

Hi lotto,
You read the question wrongly!
It is 3 / cosec^2 y not 3 / cosec^2 2y

So it would be as simple as this,
2 sin y + 1 = 3 sin^2 y
Let x= sin y
3x^2 - 2x - 1 = 0
(3x + 1) (x - 1) = 0
x = -1/3 or x = 1
sin y = -1/3 or sin y = 1
y = 360 - sin-1(-1/3) or y = 90

Good job! CHeers :celebrate:[/quote]Hi dazzlego,

Thanks for the correction.
I knew it :slapshead:
This carelessness won't leave me alone :frustrated:

[neowanz]

For proving angles, it will be better to make an angle to be alpha and start from there, that would actually have the same effect in using algebra to solve. For proving equation, starts from the theorem first (either tangent-secant theorem, intersecting chord theorem, etc)

[germalux]

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[neowanz]

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[neowanz]

Hi everyone,


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Anyway, the first question has been up and it's on Geometric Proof. Do attempt it before looking at the answer.

Have fun in doing math

[dazzlego]

Need help to solve this question


Find the possible value of X if |X+1| = 2X-3

Thanks

[dazzlego]

Can someone tell me what is the answer for this question?


Find the possible value of X if |X+1| = 2X-3

Thanks

[verykiasumummy]

dazzlego:

Need help to solve this question


Find the possible value of X if |X+1| = 2X-3

Thanks

hi dazzlego,

x=4, my ds1 told me that...

x+1 = 2x-3
1 = x-3
4 = x
x = 4

[neowanz]

verykiasumummy:

dazzlego:

Need help to solve this question


Find the possible value of X if |X+1| = 2X-3

Thanks

hi dazzlego,

x=4, my ds1 told me that...

x+1 = 2x-3
1 = x-3
4 = x
x = 4

Pls do include this also,
X+1= -(2x-3)
3x=2
X=2/3 (reject)

Thks

[dazzlego]

neowanz:

verykiasumummy:

[quote=\"dazzlego\"]Need help to solve this question


Find the possible value of X if |X+1| = 2X-3

Thanks

hi dazzlego,

x=4, my ds1 told me that...

x+1 = 2x-3
1 = x-3
4 = x
x = 4

Pls do include this also,
X+1= -(2x-3)
3x=2
X=2/3 (reject)

Thks :)[/quote]Yeah u should include that steps. Thanks neowanz and verykiasumummy :celebrate: