Homework Help: Math

Posted by House on Friday, October 3, 2008 at 1:16pm.

If a and B are two angles in Quadrant 2 such that tan a=-1/2 and tan B= -2/3, find cos(a+b)?

tan(a) = -1/2

oppsite side = 1: adjacentside = 2

hypotenuse = sqrt(1+4) = sqrt(5)

sin(a) = 1/Бу5

cos(a) = -2/Бу5

tan(b) = -2/3

opposite side = 2 and adjacentside = 3

hypotenuse = sqrt(4+9) = Бу13

sin(b) = 2/Бу13

cos(b) = -3/Бу13

cos(a+b) = cosa cosb - sina sinb

=(-2/Бу5)(-3/Бу13) - (1/Бу5)(2/Бу13)

= 6/Бу65 - 2/Бу65

= 4/Бу65

right?

Math - bobpursley, Friday, October 3, 2008 at 1:58pm
I didn't check all, but you have the technique. You can easily check these on your calculator.

Answer this Question

Related Questions

Math - If α and β are two angles in Quadrant II such that tan...
Trigonometry - 1.Solve tan^2x + tan x – 1 = 0 for the principal value(s) to...
Trig. - sec^2xcotx-cotx=tanx (1/cos)^2 times (1/tan)-(1/tan)=tan (1/cos^2) times...
Trig - Given: cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 &...
Integration - Intergrate ¡ì sec^3(x) dx could anybody please check ...
Maths Calculus Derivatives - Find the first derivative for the following ...
trig - h t t p : / / i m g 4 0 . i m a g e s h a c k . u s / c o n t e n t . p h...
math - Use the exact values of the sin, cos and tan of pi/3 and pi/6, and the ...
Maths- complex numbers - Find tan(3 theta) in terms of tan theta Use the formula...
math - Use the exact values of the sin, cos and tan of pi/3 and pi/6, and the ...

For Further Reading

First Name:
School Subject:
Answer: