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2? + kI - 20limI-5I - 5Solve for k to make it exist?

Sagot :

Answer:

k = -1

Step-by-step explanation:

The limit will exist if:

One of the roots of the equation in the numerator is 5. This happens because if this happens, we can simplify with the denominator. So

Solving a quadratic equation:

In the following format:

ax² + bx + c = 0

The solution is given by:

[tex]x=\frac{-b\pm\sqrt[]{b^2-4ac}}{2a}[/tex]

In this question:

x² + kx - 20 = 0

The solution is:

[tex]x=\frac{-k\pm\sqrt[]{k^2-4\ast1\ast(-20)}}{2}=\frac{-k\pm\sqrt[]{k^2-80}}{2}[/tex]

Since we want x = 5.

[tex]\frac{-k+\sqrt[]{k^2+80}}{2}=5[/tex][tex]-k+\sqrt[]{k^2-80}=10[/tex][tex]\sqrt[]{k^2+80}=10+k[/tex][tex](\sqrt[]{k^2+80})^2=(10+k)^2[/tex][tex]k^2+80=100+20k+k^2[/tex][tex]k^2+80-100-20k-k^2=0[/tex][tex]-20-20k=0[/tex][tex]20k=-20[/tex][tex]k=\frac{-20}{20}=-1[/tex]

k = -1