What is the discriminant of #7x^2+8x+1=0# and what does that mean?

1 Answer
Nghi N.
Jul 25, 2015

Solve #y = 7x^2 + 8x + 1 = 0#

Answer: -1 and #-1/7#

Explanation:

#D = d^2 = b^2 - 4ac = 64 - 56 = 8 > 0#. This means there are 2 real roots (2 x-intercepts).
In this case (a - b + c = 0) we'd better use the shortcut --> two real roots: -1 and # (-c/a = -1/7)#
REMINDER OF SHORTCUT
When a + b + c = 0 -> 2 real roots: 1 and c/a
When a - b + c = 0 -> 2 real roots: -1 and -c/a

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