another freebie!

another freebie! haha, what else do i remeber that was easy....
these formula's, i'm pretty sure they are for when you have an angle that they want the sin or cos of but its not on the trig chart but its the sum or difference of two angles that ARE on the trig chart.

its all about sin and cos
sin(alpha +/- beta) = sinalphacosbeta+/-cosalphasinbeta
cos(alpha +/-beta) = cosalphacosbeta -/+sinalphasinbeta

they could as you to find the exact value of cos 75
and B-rob told us that you use the cos formula above and use two trig chart angles that add or subtract to give you the anlge they want.
so you know that 45 and 30 are both trig chart angles and they ADD to give you 75, so you go to your cos formula and plug in the first part for addition, then you can look further down the formula and see that if its addtion in the front, that it'll be subtraction in the back.
you plug it in and get
cos45cos30-sin45sin30
so you use your brain the remeber the trig chart and you know this
square root of two over 2 * 1/2 - square root of 3 over 2 * square root of 2 over 2which simplifies to square root of 2 + square root of 6 all over 4

but if they give you something like this
sin15cos15-cos15sin15
you can know from the formula and from the sign inbetween that you have to ADD these two angles, which is the other side of the formula.
so you get sin 30
which is 1/2
waaaaaahoooooooo
holidays are overrr:(