Prelim 2016 Maths Help Thread (3 Viewers)

[eyeseeyou]

Find in the simplest surd form the value of:

a. tan15
b.cos15

 

[eyeseeyou]

If sin (theta)=3/4, 90 degrees is smaller than (theta) is smaller than 180 degrees, evaluate in surd form,

a. Sin2(theta)
b. cos2(theta)
c.tan2(theta)
In which quadrant does 2(theta) lie in?

 

[eyeseeyou]

1.Use expansion of sin(A+B) to evaluate sin 195
2.Simplify 1/2sin(theta)tan(theta)

 

[eyeseeyou]

I can't seem to work these easy questions out for some reason although I can work out others

 

[Drongoski]

Find in the simplest surd form the value of:

a. tan15
b.cos15

Let T stand for tan 15

tan 30 = tan (15+15) = 2T/(1-T^2) = 1/sqrt(3)



Choose the positive value.

i.e. tan 15 = 2 - sqrt(3)


For cos 15, again use a double angle formula:

2 cos²15 = 1 + cos (15+15) = 1 + sqrt(3)/2

 

[eyeseeyou]

Let T stand for tan 15

tan 30 = tan (15+15) = 2T/(1-T^2) = 1/sqrt(3)

Thanks Drongoski

Shall reward you for helping me

 

[eyeseeyou]

I do not know what I am doing wrong for the following questions:

a. sin4xcos4x
b. 1+cos(180+2(theta))
c.sinxcosxcos2x
d. 2sin2xcos2x

 

[InteGrand]

I do not know what I am doing wrong for the following questions:

a. sin4xcos4x
b. 1+cos(180+2(theta))
c.sinxcosxcos2x
d. 2sin2xcos2x

What were your attempts?

 

[eyeseeyou]

I tried it and ended up with all these weird values

iirc you have to use double andgle formula for these q's

 

[eyeseeyou]

Let T stand for tan 15

tan 30 = tan (15+15) = 2T/(1-T^2) = 1/sqrt(3)



Choose the positive value.

This cannot be right??

I used tan (45-30) and ended up getting -1/3 (I am sure this answer isn't right)

 

[InteGrand]

I used tan (45-30) and ended up getting -1/3 (I am sure this answer isn't right)

(LaTeX may take a while to load, it seems to have been that way on this site today. Basically, using that method you should get (√(3) – 1)/(√(3) + 1). How did you end up with -1/3?)

This can be simplified to 2 – √(3) by rationalising the denominator.

 

[eyeseeyou]

(LaTeX seems to be taking a while to load. Basically, using that method you should get (√(3) – 1)/(√(3) + 1). How did you end up with -1/3?)

You were supposed to use the tan rule for this question iirc

 

[InteGrand]

You were supposed to use the tan rule for this question iirc

I used a tan compound angle formula.

 

[eyeseeyou]

(LaTeX may take a while to load, it seems to have been that way on this site today. Basically, using that method you should get (√(3) – 1)/(√(3) + 1). How did you end up with -1/3?)

The answer is actually 2-Sqaureroot of 3

 

[InteGrand]

The answer is actually 2-Sqaureroot of 3

It is the same – rationalise the denominator of my answer to see this (I assume you've learnt how to do this).

 

[eyeseeyou]

It is the same – rationalise the denominator of my answer to see this (I assume you've learnt how to do this).

Thanks Integrand

Of possible please help me with my other questions

 

[eyeseeyou]

(2tantheta)/(1-tan squared theta) when theta = 22.5 degrees

sin squared 50+sin squared 40

 

[InteGrand]

1.Use expansion of sin(A+B) to evaluate sin 195
2.Simplify 1/2sin(theta)tan(theta)

1) Do sin(195°) = sin(135° + 60°), for example, since we know the values of trig. functions at 135° and 60°.

 

[eyeseeyou]

1) Do sin(195°) = sin(135° + 60°), for example, since we know the values of trig. functions at 135° and 60°.

Thanks what about the second part?

 

[eyeseeyou]

If sin (theta)=3/4, 90 degrees is smaller than (theta) is smaller than 180 degrees, evaluate in surd form,

a. Sin2(theta)
b. cos2(theta)
c.tan2(theta)
In which quadrant does 2(theta) lie in?

1.Use expansion of sin(A+B) to evaluate sin 195
2.Simplify 1/2sin(theta)tan(theta)

Did someone forget these 2?