Question

24-25题要解题过程

Answer 1

(6)
f(x)
=cos2x+6cos(π/2-x)
=[1-2(sinx)^2 ] + 6sinx
= 11/2 -2(sinx -3/2)^2
max f(x) = 11/2 -2(1/2)^2 = 11/2 - 1/2 = 5
ans :B
(25)
(1)
c=√3a.sinC - c.cosA
=√3c.sinA - c.cosA
1=√3sinA - cosA
1=2sin(A-π/6)
sin(A-π/6) = 1/2
A-π/6 = π/6
A =π/3
(2)
a=2 ,SΔABC=√3
To find : b, c
SΔABC=√3
(1/2)bc.sinA =√3
(1/2)bc.(√3/2) =√3
bc = 4 (1)
a^2=b^2+c^2-2bc.cosA
4=b^2+c^2 - 2(4)cos(π/3)
4=b^2+c^2 - 4
b^2+c^2 = 8
(b+c)^2 -2bc = 8
(b+c)^2 = 16
b+c =4 (2)
from (1) and (2)
b+ 4/b =4
b^2-4b+4 =0
b=2
from (2) =>c=2
ie
(b,c)=(2,2)

Answer 2

数学就要多思考自己做，不会做，就把必要的写下来，不能依赖别人！要不就会行成惰性，到最后最基础的思考题都不会！记住，业精于勤荒于嬉，行成于思毁于随！