7 uždavinys

Išspręskite lygtį (x - 3)(x - 7) = 21.

A 3 ir 7

B 0 ir 10

C 10

D Sprendinių nėra

Sprendimas:

(x-3)* (x-7) =
21

(x-3)* (x-7) = 21 $(x-3)\cdot (x-7)$ = $21$

( x* x- x* 7- 3* x+ 3* 7) = 21 $(x\cdot x-x\cdot 7-3\cdot x+3\cdot 7)$ = $21$

( x^²- x* 7- 3* x+ 3* 7) = 21 $(x^{2}-x\cdot 7-3\cdot x+3\cdot 7)$ = $21$

( x^²- 10* x+ 3* 7) = 21 $(x^{2}-10\cdot x+3\cdot 7)$ = $21$

( x^²- 10* x+21) = 21 $(x^{2}-10\cdot x+21)$ = $21$

x^²- 10* x+21 = 21 $x^{2}-10\cdot x+21$ = $21$

x^²- 10* x = 21-21 $x^{2}-10\cdot x$ = $21-21$

x^²- 10* x = 0 $x^{2}-10\cdot x$ = 0

x = 0 $x$ = 0

x-10 = 0 $x-10$ = 0

x = 0+10 $x$ = $0+10$

x = 10 $x$ = $10$

Atsakymas: B