Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2007-11-13 04:32:54

lisa123
Member
Registered: 2007-11-11
Posts: 5

pre calculus

I am having trouble with the topic
the question is find all the sine, cosine and tangent of alpha if sec alpha = -4sqrt5/5 and is in the second quadrant.

Offline

#2 2007-11-13 08:00:28

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

Re: pre calculus

Let β = π − α, so β is acute and cos(β) = −cos(α).

Draw a right-angled triangle with hypotenuse

, one of the other sides 1 and the angle in between β. Then you have

The length of the third side can be found by Pythagoras’ theorem; it is

So now you know all three sides of the right triangle, you should be able to work out the sine, cosine and tangent of β. Finally, since α is in the second quadrant, sine will be positive while cosine and tangent are negative, so adjust your signs accordingly for the sine, cosine and tangent of α.

Offline

Board footer

Powered by FluxBB