Question

how many terns of the series 42,36,30.....amount to 150​

Answer 1

Answer:

a=42

d=-6

sn=150

n=?

sn=n/2(2a+(n-1)d)

n/2(84+(n-1)-6)

n/2(84-6n+6)

n/2(90-6n)

n(45-3n)

45n-3n^2=150

then u find the n

Answer 2

Answer:

You can simply solve it by using formula of AP .

150=n/2 (2a +(n-1)d

150=n/2 (2*42 + n-1) -6

150=n(42-3n +3)

150=42n-3n^2+3n

by solving quadratic equation we get n=15

how to solve quadratic equation is in attachment

Explanation:

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