(1)下列等式中正确的一组是
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(1)下列等式中正确的一组是
A.cos45°<cos90°<cos135° B.cos45°>cos90°>cos135°
C.cos45°<cos135°<cos90° D.cos45°>cos135°>cos90°
(2)cos(-19/4π)+cos5/6π
(3)若f(x)=ax+bsinx=1(a,b为常数)满足f(5)=7,求f(-5)的值
第三题是 若f(x)=ax+bsinx+1(a,b为常数)满足f(5)=7,求f(-5)的值
A.cos45°<cos90°<cos135° B.cos45°>cos90°>cos135°
C.cos45°<cos135°<cos90° D.cos45°>cos135°>cos90°
(2)cos(-19/4π)+cos5/6π
(3)若f(x)=ax+bsinx=1(a,b为常数)满足f(5)=7,求f(-5)的值
第三题是 若f(x)=ax+bsinx+1(a,b为常数)满足f(5)=7,求f(-5)的值
(1)B
(2)cos(-19/4π)+cos5/6π
=cos(4π+3/4π)+cos5/6π
=cos3/4π+cos5/6π
=cos135°+cos150°
=-√2/2-√3/3
=-√2+√3/2
(3)∵f(5)=5a+bsin5+1=7 =>5a+bsin5=6
f(-5)=-5a+bsin(-5)+1 =>-5a-bsin5+1
=-(5a+bsin5)+1
=-6+1
=-5
(2)cos(-19/4π)+cos5/6π
=cos(4π+3/4π)+cos5/6π
=cos3/4π+cos5/6π
=cos135°+cos150°
=-√2/2-√3/3
=-√2+√3/2
(3)∵f(5)=5a+bsin5+1=7 =>5a+bsin5=6
f(-5)=-5a+bsin(-5)+1 =>-5a-bsin5+1
=-(5a+bsin5)+1
=-6+1
=-5