Write the quadratic equation in standard form and then choose the value of "b." (2x - 1) (x + 5) = 0

If we were to foil

after experieence

we know

ax²+bx+c=0

and

in form

(ax+b) (cx+d) = 0

if we expand it, we get

acx²+bcx+adx+bd=0

or

(ac) x² + (bc+ad) x + (bd) = 0

compare to

ax²+bx+c=0

we notice that the middle terms (x terms) are

b = (bc+ad)

so

in form

(2x-1) (1x+5)

b=bc+ad = (-1*1+2*5) = - 1+10=9

b=9

or you could just expand it