plz help !! wat is x^3+x^2=700 to 2 dp ???

Answer 1

Start with an integer search

try x = 5 ..... 5^3 + 5^2= 150 ...too small
try x = 8..... 8^3 + 8^2 = 576 ...toosmall
try x = 9..... 9^3 + 9^2 = 747...too large but nearer tha x = 8

now move to 1dp value

try x = 8.9.... 8.9^3 + 8.9^2 = 784.179 too big
try x = 8.8.... 8.8^3 + 8.8^2 = 758.912 too big
try x = 8.6.... 8.6^3 + 8.6^2 = 710.16 too big
try x = 8.5.... 8.5^3 + 8.5^2 = 686.375 too small

Solution is between 8.5 and 8.6 and probably nearer 8.6

now move to 2dp values

try 8.56 8.56^3 + 8.56^2 = 700.49 too large
try 8.55 8.55^3 + 8.55^2 = 698.13 too small

to decide which of these is the 2dp value try the mid point 8.555

Being a cubic there may be two more values which you can find using this technique

Answer 2

Ive worked out 2 dp is two decimal places, but thats it.....

Answer 3

Think there is only one real answer and two complex roots.

Answer between 8 and 9. Then could apply Newton's method to get better approximation until get within two d.p.s.

Else apply other tecniques you have been taught to do this.

Answer 4

Agreed 8.56

Check 8.56 cubed = 627

8.56 squared = 73

Total = 700

Answer 5

what does "to 2 dp?... if i knew that i could do it

Answer 6

By guess-and-check:
x ≈ 8.56
There are also 2 complex roots.

Answer 7

Take solace in the fact that you are not the only one to have absolutley no idea.

Answer 8

just so you know... because this is a 3rd order polynomial, there will be up to 3 seperate answers for x.

Answer 9

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Answer 10

x=8.56