First term ,a=4 , common difference =4-7=-3, n =50
sum of first 50terms= (50/2)[2×4+(50-1)(-3)]
=25×[8+49]×-3
=25×57×-3
=25× -171
= -42925
derivation of the formula for the sum of n terms
Progression, S
S=a1+a2+a3+a4+...+an
S=a1+(a1+d)+(a1+2d)+(a1+3d)+...+[a1+(n−1)d] → Equation (1)
S=an+an−1+an−2+an−3+...+a1
S=an+(an−d)+(an−2d)+(an−3d)+...+[an−(n−1)d] → Equation (2)
Add Equations (1) and (2)
2S=(a1+an)+(a1+an)+(a1+an)+(a1+an)+...+(a1+an)
2S=n(a1+an)
S=n/2(a1+an)
Substitute an = a1 + (n - 1)d to the above equation, we have
S=n/2{a1+[a1+(n−1)d]}
S=n/2[2a1+(n−1)d]
Answer:
16x² +48x +36
Step-by-step explanation:
A perfect square trinomial is of the form ...
(a +b)² = a² +2ab +b²
We want to match this form.
__
<h3>comparing terms</h3>
Comparing the known terms, we see ...
16x² = a² ⇒ a = 4x
36 = b² ⇒ b = 6
<h3>filling in the missing term</h3>
The missing term is the linear term:
2ab = 2(4x)(6) = 48x
? = 48
