1) (1-√15)(1+√15)=1² - (√15)² = 1-15 = -14
2) √0.002 * √12.8 = √(0.001*2) * √(2*6.4)=√2*√2*√0.001*√6.4=
=2*√(0.001*0.1*64)=2*√64*√0.0001=2*8*0.01=16*0.01=0.16
3) =24*√13 * √13 = 24*13 = 24/6 = 4
13*√3 * √12 13*√36
4) 61 -7y +1=14
9
61-7y=14-1
9
61-7y=13*9
61-7y=117
-7y=117-61
-7y=56
y= -8