(2)(x+y)/ 10

6.b(H+20)C(H-30)(H+20)-(H-30)= 20+30 = 50。

7.s length = 2x * 4 = 8x s step = 5 (x+3x)/2 = 10x.

8x is less than 10x 10x-8x = 2x.

8.c( 1)= 2 pie r * 2 = pie R.

c(2)= 2 pai r+2 pai( 1/2+ 1/3+ 1/6)r = 4 pai r

( 1)=(2)

9.(a+ 1)(a+3- 1)=(a+2)m = a+(n- 1)m = 20+ 19- 1 = 38

10.( 10a+b)+( 10 b+a)= 1 1a+ 1 1b = 1 1(a+b)

Because both a and b are positive integers, (a+b) is a positive integer.

So this number can be divisible by 1 1.

13. solution: let the second internal angle be x degrees.

x+3x+x+ 15= 180 x=33

33*3=99 33+ 15=48