Question

11. Given that fo (-1, - 2) = f(-1, - 2) = 0, L (1, - 2) = = 6 and fa (1, - 2)
Joy (-1, - 2) - $2(-1, - 2) = 72. Then the function Shas
(A) minimum
(B) maximum
(C) Both maximum and minimum (D) None of these
at (-1, -2).
REDMI NOTE​

Answer 1

Answer:

Step-by-step explanation:

Just add eqn 1 and 2.

50B = 300 ......B = 6

Let's find A now. Since you know B =6. You could assume the B term as some known number which we are going to find out.

The key to solving is trying to get rid of other variables and solve for single variable. By adding 1 and 2 I knew I could get rid of A and C terms.

Now using 2 and 3. What if I multiply eqn2 by 6 and eqn3 by 5?

Do you notice that my C term will become -30 in eqn2 and 30 in eqn 3.

There was a 5C in 2 and 6C in 3. If I wanted to make coefficients of C equal in both equation, i do

6Xeqn2 : -750A+150B-30C =0 = -750A+900 -30C

5Xeqn3 : 1080A+180B+30C=0 = 1080A+1080+30C

SUM : 330A+1980 = 0 ......A=-6

Remember you already know B=6. That's how 900 and 1080 came.

You know A and B. Now put them in any one of the three equations to get C. Let's try eqn3

216A + 36B + 6C = -1296+216+6C =0 .......C = 180

Remember always try to multiply equations in such a way that after adding or subtracting one variable is gone. If you do that in a way among such all equations, you ll be able bring it down to single variable and start solving back for all others using this same methodology