verify trig identities

jjulander

New member
Joined
Oct 13, 2005
Messages
2
Need some more help with these:

(1 + sec (-x))/ (sin(-x) + tan(-x)) = -csc x

and

(cot x)/ (csc x -1) = (csc x +1)/ (cot x)[/u]
 
Remember odd and even functions?


Sec(-x)=Sec(x) because Sec is even

Sin(-x)=-Sin(x) because Sin is odd

Tan(-x)=-Tan(x) because Tan is odd


(1 + sec (-x))/ (sin(-x) + tan(-x))


So we rewrite the left side as

(1+sec(x))/(-sin(x)-tan(x))

From here you have a couple options, I think, but I would convert everything to sin and cos.

(1+(1/cos(x))/(-sin(x)-(sin(x)/cos(x)))

Now, find the LCD's

((cos(x)+1)/cos(x))/((-sin(x)cos(x)-sin(x))/cos(x)


Now, remember that dividing is the same as multiplying by the reciprocal.

[cos(x)+1]/cos(x) X cos(x)/[-sin(x)cos(x)-sin(x)]

Cosines cancel, so we get:

[cos(x)+1]/[-sin(x)cos(x)-sin(x)]


Now we factor out the -sin(x) in the denominator.

[cos(x)+1]/[-sin(x)(cos(x)+1)]


Now it's simple: cos(x)+1 in the numerator and denominator, so they cancel, and we get:

1/-sin(x)=-csc(x)



Try doing the second problem on your own using these techniques.
 
Top