How do you solve...0=-5t^2+20t+1

1 answer:

4 0

There were 2 solutions that i came up with. Here is the first one. I rearranged the eqaution by subtracting what is to the right of thr equal sign. Multiply the coefficeint of the first term by the constant 5 x (-1)= -5. Then you would find 2 factors of -5 whose sum equals the coefficient of the middle term which is 20. -5+1= -4 and -1+5=4. the eqaution then comes to 5t^2-20t-1=0. you would solve 5t^2-20t-1=0. you would divide both sides of the equal sign by 5. t^-4t-1/5=0. then t^2-4t=1/5. add 4 to both sides of the equation. so we get 21/5+ 4 + 4t -t^2=21/5. it then comes out to be t^2-4t+t=t-2^2. according to the law of transitivity it is t-2^2=21/5.

t =(20+√420)/10=2+1/5√ 105 = 4.049 .

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50+51+52+...+101=... Can you help me? I do not understand

Dmitriy789 [7]

Suppose

$S=50+51+52+\cdots+100+101$

At the same time, we can write

$S^*=101+100+99+\cdots+51+50$

Note that $S=S^*$ (just reverse the sum). Let's pair the first terms of $S$ and $S^*$ , and the second, and the third, and so on:

$S+S^*=(50+101)+(51+100)+(52+99)+\cdots+(100+51)+(101+50)$

Now, each grouped term in the sum on the right side adds to 151. There are 52 grouped terms on that same side (because there are 50 numbers in the range of integers 51-100, plus 50 and 101), which menas

$S+S^*=52\cdot151$