Posted by Solly on Tuesday, May 10, 2011 at 2:48am.
Cos70cos10+sin70sin10 e =2cos^2 2x1

Maths  Reiny, Tuesday, May 10, 2011 at 7:24am
Cos70cos10+sin70sin10 e =2cos^2 2x1
don't know what that "e" is supposed to be, seems to be superfluous.
recall : cos (AB) = cosAcoB + sinAsinB
Cos70cos10+sin70sin10 =2cos^2 2x1
cos(7010) = 2cos^2 2x  1
cos60 = 2cos^2 2x  1
recall cos 2A = 2cos^2 A  1
so 2cos^2 2x  1 = cos 4x
cos 4x = cos60
4x = 60° or 4x = 300°
x = 15° or x = 75°
since cos 2x has a period of 180°
other solutions would be
x = 15+180 = 195°
or
x = 75+180 = 255°
Answer This Question
Related Questions
 Math  Determine the solution of the equetion: 2cos x1=0? 2cos x=0? and 2cos x+...
 math  cosA= 5/9 find cos1/2A are you familiar with the halfangle formulas? the...
 Maths  y = 14sin(8x)2cos(5x)  4sin(5x)cos(8x) u = 14sin(8x) u' = 112cos(8x...
 Maths  How do you derive: 2cos(32x)?
 maths  solve for x if 2cos(x30)=1, £(90;270)
 Maths  solve the following eq. [0<=x<=360] 2cos(3x72)=1
 maths  2cos^2a*cos^2b+2sin^2asin^2b1=cos2acos2b
 Trigonometry  Need help solving problems using the Trigonometric Identities: ...
 Maths  y = 2[cos1/2(f1  f2)x][cos1/2(f1 + f2)x] let f1 = 16 let f2 = 12 ...
 maths  give the solution of the initialvalue problem dy/dx=(1+2cos^2(x))/y, (y...
More Related Questions