(4/5)*√(5/8)*√90 =(4/5)*√((5/8)*90) =(4/5)*√((5/8)*5*2*3²) =(4/5)*(5*3/2) = 6.
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(√0,002) *(√12,8) =√(0,002 *12,8) =√2*2*64*10^(-4) =2*8*10 ^(-2) =0,16.
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(√2,5) *(√0,9) =√(2,5 *0,9) =√( (25 *9)/10²) =5*3/10 = 1,5 .
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(4-√2)/(4+√2) -(4+√2)/(4 -√2) =( (4-√2)² -(4+√2)² ) /(4+√2)(4-√2) =
((4-√2 -(4+√2))(4-√2 +4+√2)/(4+√2)(4-√2) = (-2√2*8)/ (4² -(√2)²) = -16√2/(16-2)=
-(16√2)/ (14) = -(8√2)/7.
* * * P.S. * * * *
(4-√2)² -(4+√2)² || можно и так || =4²-2*4*√2+(√2)² -(4²+2*4*√2+(√2)²)=
4²-2*4*√2+(√2)² -4²-2*4*√2-(√2)²= -2*(2*4*√2) = - 16√2