Question

Помогите пожалуйста 

[tex](3- sqrt{2})*(5+ sqrt{8})=?
 (4- sqrt{3})*( sqrt{3}+6)=?
 (2+ sqrt{15})*( sqrt{5}- sqrt{3} =?
 (3 sqrt{5}+ sqrt{3)}*( sqrt{3}-4 sqrt{5}=?
 (x- sqrt{y})*(3x-4 sqrt{y} )=?
 ( sqrt{x} +3 sqrt{y})*( sqrt{y}-4 sqrt{x} )=?
 (2 sqrt{a}+ sqrt{b})*( sqrt{a}-5 sqrt{b})=?
 (4 sqrt{a}-7 sqrt{b})*(2 sqrt{b}-3 sqrt{a})=?

Answer 1

$(3- sqrt{2})*(5+ sqrt{8})=15+3sqrt8-5sqrt2-sqrt{16}=\ =15+6sqrt2-5sqrt2-4=11+sqrt2\ \ (4- sqrt{3})*( sqrt{3}+6)=4sqrt3+24-3-6sqrt3=21-2sqrt3\ \ (2+ sqrt{15})*( sqrt{5}- sqrt{3}) =2sqrt5-2sqrt3+sqrt{75}-sqrt{45}=\ =2sqrt5-2sqrt3+5sqrt{3}-3sqrt{5}=3sqrt3-sqrt5$

$(3 sqrt{5}+ sqrt{3)}*( sqrt{3}-4 sqrt{5})=3sqrt{15}-12*5+3-4sqrt{15}=\ =-sqrt{15}-57\ \ (x- sqrt{y})*(3x-4 sqrt{y} )=3x^2-4xsqrt y-3xsqrt y+4y=3x^2+4y-7xsqrt y\\ ( sqrt{x} +3 sqrt{y})*( sqrt{y}-4 sqrt{x} )=sqrt{xy}-4x+3y-12sqrt{xy}=3y-4x-11sqrt{xy}\ \ (2 sqrt{a}+ sqrt{b})*( sqrt{a}-5 sqrt{b})=2a-10sqrt{ab}+sqrt{ab}-5b=2a-5b-9sqrt{ab}\ \ (4 sqrt{a}-7 sqrt{b})*(2 sqrt{b}-3 sqrt{a})=8sqrt{ab}-12a-14b +21sqrt{ab}=\=29sqrt{ab}-12a-14b$