sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2 sin30=1/2
m If x is a positive angle smaller than 180° and cos(x) = -1/3, then sin(x) =
A) -2/3 B) 2√2 / 3 C) 8/9 D) -8/9 E) 4/9
A) -2/3 B) 2√2 / 3 C) 8/9 D) -8/9 E) 4/9
m
cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2 cos60=1/2
I hadn't answered before to see if anyone else was gonna answer because I don't wanna be the only one who answers the problems of the week.
ReplyDeleteThe answer is c) because:
90º<x<180º, so 2nd quadrant, so cos is negative and sine positive.
sin^2 + cos^2 = 1; We solve it and we get sine = 8/9
Imanol's explanation is good and easy to understand, but he's commited a mistake on the last equation. 8/9 is not the sine, it's the sin^2. So, to complete the equation, you must calculate the square root of 8/9, that is the option b.
ReplyDeleteNicolás, you are right. Imanol told me the right solution last wednesday, but he didn´t post it to provoke discussion. Thank you both for your interesting ideas.
ReplyDeleteThe function sine is positive in the first and second quadrant.
ReplyDelete