Question

2) (y-2)(y+2)+(3-y)(3+y)

3) (a+b)(a-b)-(a-b)^2

Answer 1

2) $(y-2)(y+2)+(3-y)(3+y)=y^{2}-4+9-y^{2}=(y^{2}-y^{2})+(9-4)=5$

 

3) $(a+b)(a-b)-(a-b)^{2}=a^{2}-b^{2}-(a^{2}-2ab+b^{2})=a^{2}-b^{2}-a^{2}+2ab-b^{2}=(a^{2}-a^{2})+2ab+(-b^{2}-b^{2})=2ab-2b^{2}$

 

Answer 2

2) (y-2)(y+2)+(3-y)(3+y)  =  y² - 2²   +   3²- y²  = - 2²   +   3²  = - 4 + 9= 5

3) (a+b)(a-b) - (a-b)² = a²-b² - (a²-2ab +b²) = a² - b² - a² + 2ab - b² =

= 2ab - 2b²