2A+B=4X+7 A+2B=5X-1 A×2B=?

Sol
(2A+B)+(A+2B)=(4X+7)+(5X－1)
3A+3B=9X+6
A+B=3X+2
(2A+B)－(A+B)=(4X+7)－(3X+2)
A=X+5
(A+2B)－(A+B)=(5X－1)－(3X+2)
B=2X－3
A*(2B)
=(X+5)*(4X－6)
=X(4X－6)+5(4X－6)
=(4X^2－6X)+(20X－30)
=4X^2+14X－30

4X平方+14X-30

2A+B=4X+7 i
A+2B=5X-1 ii
2*i, 4A+2B=8x+14 iii
iii-i, 3A=3x+15
A=x+5
put A=x+5 into ii
x+5+2B=5x-1
2B=4x-6
A*2B
=(x+5)(4x-6)
=4x^2 -6x+20x-30
=4x^2 +14x-30