Which equation has exactly two real and two nonreal solutions? a.)x^4-49x^2=0 b.)x^3+2x^2+x-7=0 c.)x^3-5x^2-x+12=0 d.)x^4-48x^2-49=0 calculate s24 for the arithmetic sequence in which a13=1.9 and the common difference is d=3.7

D.
first, eliminate B and C, because the highest degree in these two equation is 3, a 3-degree equation has 3 roots, not 4. 

between A and D, A has the roots 0, 0, 7, and -7, all real roots.

D can be factored into (x²-49)(x²+1)=0
x²=49 or x²=-1
x=7 or -7, x=i or -i    two real roots, two unreal roots 

for the second equation: 
first, find the first term by using the formula:
the nth term=the first term + (n-1)*difference
you are given the 13th term and d=3.7
a13=a1+(13-1)d
1.9=a1+12*3.7
a1=-42.5

the sum of the first 13 terms is S=(a1+a13)*(13/2)=(-42.5+1.9)*6.5=-263.9