79.
1) (√3 -1)(√3 +1)=(√3)² -1² =3-1=2
2) (√5 +√3)(√5 -√3)=(√5)² -(√3)² =5-3=2
3) (2√7 -√6)(2√7 +√6) =(2√7)² -(√6)² =4*7 -6 =28-6=22
4) (√3 -2√10)(√3 +2√10) =(√3)² -(2√10)² =3 -4*10 =3-40=-37
На фото.......................
... = (y(4x - 3y) + x² + 3y²)/xy = (4xy - 3y² + x² + 3y²)/xy = (x² + 4xy)/xy = (x + 4y)/y = 4 + x/y.
<span> 1/2+3/14+2/7=7/14+3/14+4/14=14/14=1</span>