2s﹙5— 10)=s5+s﹙ 10- 15﹚

∵s﹙5— 10)= 100-30=70,s5=30,s 10= 100

∴2×70=30+S﹙ 10- 15﹚

140-30=s﹙ 10- 15﹚

1 10=s﹙ 10- 15﹚

That is, s (10-15) =110.

∶s 15=s 10+s﹙ 10- 15﹚= 100+ 1 10=2 10

2 solution: point (. x，。 Y) On the regression line, calculate. X =2 and. y = 4.5

Substitution of a = 2.6;

So the answer is 2.6.

3 solution: from the meaning of the question,1/5 (a+0+1+2+3) =1,and a= 1 is obtained.

∴ The sample variance is S2= 1/5? [(- 1- 1)2+(0- 1)2+( 1- 1)2+(2- 1)2+(3- 1)2]=2,

4.a (crossing or non-plane)

5 tanx = sinx/cosx =(-3/5)/(4/5)=-3/4

6A={y|y=log3？ x，x & gt 1 } = { y | y & gt； 0}

B={y|y=3x，x & gt0 } = { y | y & gt0}

So a ∩ b = {y | y > 0}

? So choose? , there is no this option. . .

? Hope to adopt ~ ~! Ask again if you don't understand ~!