1) 3sin(x+10°)+5sin(x+70°)
=3sinx*cos(10°)+3cosx*sin(10°)+5sinx*cos(70°)+5cosx*sin(70°)
=sinx*(3cos(10°)+5cos(70°))+cosx*(3sin(10°)+5sin(70°))
而asinx+bcox的最大值为√(a^2+b^2),所以3sin(x+10°)+5sin(x+70°)的最大值为
√((3cos(10°)+5cos(70°))^2+(3sin(10°)+5sin(70°))^2)
=√(34+30( cos(10°)cos(70°)+sin(10°)sin(70°) )
=√(34+30( cos(10°-70°) )
=√(34+30( cos(-60°) )
=√(34+30( cos(60°) )
=√(34+30*1/2)
=√49
=7
2、直角三角形,选B.显然b+c=a意味着有两边的长度平方和等于第三边的平方.