Question

For what values of m does the graph of y = 3x^2 + 7x + m have two x-intercepts? a) m>12/49 b) m<12/49 c) m<49/12 d) m&gt; 49/12

Answer 1

The quadratic formula, has a part we call the "discriminant" defined by the variables that are inside the square root, and is denotated by "delta":

Δ=b2−4ac Whenever we solve a quadratic equation that is complete and we analyze the discriminant, we can get 3 scenarios: if→Δ>0=>∃x1,x2/ax2+bx+c=0 This just means: "if the discriminant is greater than zero, there will exist two x-intercepts" And for the second scenario: if→Δ=0→∃xo/ax2+bx+c=0 This means: "if the discriminant is equal to zero, there will be one and only one x-intercept" And for the last scenario: if→Δ<0→∃x∉R/ax2+bx+c=0 This means that :"if the discriminant is less than zero, there will be no x-intercepts" So, if we take your excercise and analyze the the discriminant: 3x2+7x+m=y we will find the values that satisfy y=0 : 3x2+7x+m=0 And we'll analyze the discriminant: Δ=72−4(3)(m) And we are only interested in the values that make the discriminant equal zero: 72−4(3)(m)=0 All you have to do is solve for "m".