What is the 22nd term of the arithmetic sequence where a1 = 8 and a9 = 56?

Question

anonymous · Answer

134
	142
	150
	158

anonymous · Answer

@campbell_st @ranga

anonymous · Answer

answers a22= 134 a41=-145

campbell_st · Answer

well the formula is 

$$a_(n) = a_{1} + (n - 1)\times d$$

you'll need this to find the common difference d

$$56 = 8 + (9 -1) \times d$$

solve for d

then use the formula again with n = 22 to find the 22nd term

anonymous · Answer

so 56 = 16(d)

Divide both sides to get d? @campbell_st

campbell_st · Answer

well you have 

56 = 8 + 8d

sbutract 8 from both sides


48 = 8d

now solve for d

anonymous · Answer

d=6

campbell_st · Answer

thats right so you now need

$$a_{22} = 8 + (22 -1) \times 6$$

anonymous · Answer

so then its
a(n)=a1+(n−1)×d
a22=8+(22−1)×6
a22 = 8 + 126
a22 = 134

campbell_st · Answer

well done

anonymous · Answer

Thank you! @campbell_st 

Seriously, I didn't understand the whole equation thing until I got your help on this one. I seriously just had that click!

campbell_st · Answer

glad to help