## anonymous one year ago Could someone explain how to do these problems? Find the first six terms of the sequence. a1 = -3, an = 2 ● an-1

1. Nnesha

n = term that you have to find so to find 2nd term replace n by 2

2. anonymous

a1=-3

3. Nnesha

$\huge\rm, a_1=3$ $\huge\rm a_n=2 \times a_{n-1}$ substitute n for 2 $\huge\rm a_n=2 \times a_{2-1}$ 2-1 = 1 then substitute a_1 for -3

4. anonymous

Ok so...would it be: -3, -6, -12, -24, -48, -96 @Nnesha

5. Nnesha

:)

6. anonymous

$a_{1}=-3$$a_{n}=2 \times a_{n-1}$ That is to say each term is equal to twice the previous term, if you are given the first term as -3 u can calculate upto as many terms as u like, each successive term is twice the last term second term will be 2 times the first time, 3rd term will be 2 times 2nd term and so on

7. anonymous

looks good!

8. anonymous

Could you help me with another one? @Nishant_Garg

9. anonymous

Find the standard form of the equation of the parabola with a focus at (0, 6) and a directrix at y = -6. @Nishant_Garg I never know quite where to start.

10. anonymous

hm I think the equation will be $x^2=4ay$ Becuase the focus lies on the y axis, the equation must be either the form of $x^2=4ay$ Or $x^2=-4ay$ But since the equation of directrix has a minus sign, it implies the the equation should be the first one |dw:1439736294431:dw| The first figure makes sense because the directrix is suppose to be like in front the parabola Also you are given $a=6$

11. anonymous

so just plug that a into the equation

12. anonymous

Thank you!