1 3 sec
2x-5 tan x-5=0
3 tan
2x+3-5 tan x-5=0
3 tan
2x-5 tanx-2=0
(3 tanx+1)(tan x-2)=0
x=180
on+(tan
-1 -1/3) or 180
on+tan
-1 2 where n is an integer---其實我習慣用radian,不過也是用degree算
2. 我覺得可能是寫錯吧---所以用了上面的計
sinC = (sin A + sinB) / (cos A + cos B)
sin C = 2sin[(A+B)/2]cos[(A-B)/2]/2cos[(A+B)/2]cos[(A-B)/2]
sin C = tan[(A+B)/2]
sinC = tan(90
o-C/2) since ABC is a triangle (0
o<C/2<90
o)
2sin
2(C/2)=1
sin(C/2)=2
-0.5 since ABC is a triangle,the negative value is then rejected
C/2=45
o or 135
o (rejected) since ABC is a triangle
C=90
o ABC is a right-angled triangle with the right angle C
[ athrun在2009-08-30 22:49重新編輯此帖 ]