Question

Va rog ajutati-ma!Dau coroana!
1.Se știe ca x+y=7.Calculati:
a)3x+3y=3(x+y)
b)-2x-2y=....
c)S=(x+y)-(2x+2y)+(3x+3y)-(4x+4y)+...+(49x+49y)-(50x+50y)
2.Se stie ca x-y+2z=5
S=(x-y+2z)+(2x-2y+4z)+...+(10x-10y+20z)

Answer 1

Răspuns:

Explicație pas cu pas:

x + y = 7

a)  3 x + 3 y = 3 ( x + y ) = 3 × 7 = 21

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b)  - 2 x - 2 y = - 2 ( x + y) = - 2 × 7 = - 14

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c)  

S = ( x + y ) - 2( x + y) + 3 ( x + y ) - 4(x +y)+.....+ 49( x + y) - 50 ( x + y)

S = ( x + y ) ( 1-2 + 3-4 + .... + 49 - 50 )

S = 7 × ( - 1 - 1 - 1 - .......- 1 )

S = 7 × ( - 25 )

S = - 175

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2)  x - y + 2 z = 5

S = (x - y + 2 z) + 2(x - y + 2 z) + ..... + 10( x - y + 2 z )

S = ( x - y + 2 z ) ( 1 + 2 + 3 + ... + 10 )

S = 5 × 10 × ( 1 + 10 ) : 2

S = 5 × 5 × 11

S = 5 x 55

S = 275