The answers (2,5) because
This is another way to do it. 2,709 welcome
Sum of n terms = a1 (r^n-1/ (r-1)
Sum of first one = 3 * (4^5 - 1) / 3 = 1023
.. 2nd = 5 * (6^2 - 1) / 5 = 35
.. 3rd = 5 ^4 - 1 / 4 = 156
.. 4th = 4 * (5^4 - 1) / 4 = 624
So in increasing order its 2nd, 3rd, 4th and first.
Since B is perpendicular to A. We can say that the gradient of B will be -1/7 (product of the gradients of 2 perpendicular lines has to be -1).
Now we know that the equation for B is y=-(1/7)x + c with c being the y intercept.
Since the point isnt specified in the question, we could leave the equation like this.
But if there is a given point that B passes through, just plug in the x and y values into their respective places and solve to find c. That should give you the equation for b.
Now, to find the solution of x, we have 2 equations:
1) y=7x+12
2)y=-(1/7)x+c
In this simultaneous equation we see that y is equal to both the expressions. So,
7x+12=-(1/7)x+c
Now, since the value of c is not found, we cannot actually find the value of x, but if we would find c, we could also find x since it would only be a matter of rearranging the equation.
And there you go, that is your solution :)