So unsure of my answer, plz help!

[karipeters]

Consider that the age, x, of a unicorn in human equivalent years can be given by the formula f(x) = - 0.001218x4 + 0.082326x3 – 1.3267x2 + 12.46x + 4.914. When a unicorn is 2.5 years old, what is its age in human equivalent years? I'm I doing this right??


f(x) = - 0.001218x⁴ + 0.082326x³ – 1.3267x² + 12.46x + 4.914
f(2.5) = -0.001218(2.5) ⁴ + 0.082326(2.5) ³ – 1.3267(2.5) ² + 12.46(2.5) + 4.914
= -0.001218(39.0625) + 0.082326(15.625) – 1.3267(6.25) + 12.46(2.5) + 4.914
= -0.047578125 +1.28634375 –8.291875 + 31.15 + 4.914
= 1.23876563 – (-7.05310937) + 24.096890625 + 29.01089025
= 8.291875 + 32.388765625 + 61.399655875
= 40.680640625 + 61.399655875
= 102.0802965
Answer:102.0802965

 

[Deleted member 4993]

Consider that the age, x, of a unicorn in human equivalent years can be given by the formula f(x) = - 0.001218x4 + 0.082326x3 – 1.3267x2 + 12.46x + 4.914. When a unicorn is 2.5 years old, what is its age in human equivalent years? I'm I doing this right??


f(x) = - 0.001218x⁴ + 0.082326x³ – 1.3267x² + 12.46x + 4.914
f(2.5) = -0.001218(2.5) ⁴ + 0.082326(2.5) ³ – 1.3267(2.5) ² + 12.46(2.5) + 4.914
= -0.001218(39.0625) + 0.082326(15.625) – 1.3267(6.25) + 12.46(2.5) + 4.914
= -0.047578125 +1.28634375 –8.291875 + 31.15 + 4.914 <<<<< Correct upto here

= 1.23876563 – (-7.05310937) + 24.096890625 + 29.01089025 <<<< How did you get this line from above?
= 8.291875 + 32.388765625 + 61.399655875
= 40.680640625 + 61.399655875
= 102.0802965
Answer:102.0802965

.

 

[karipeters]

.

-0.047578125 +1.28634375=1.23876563
1.23876563– (–8.291875)=(-7.05310937)
-7.05310937+ 31.15=24.096890625
24.096890625+4.914=29.01089025
Giving me 1.23876563 – (-7.05310937) + 24.096890625 + 29.01089025=

1.23876563 – (-7.05310937) =8.291875
8.291875+24.096890625= 32.388765625
32.388765625+ 29.01089025=61.399655875
Giving me 8.291875 + 32.388765625 + 61.399655875

8.291875 + 32.388765625=40.680640625
40.680640625 +61.399655875=102.0802965
Giving me the answer of 102.0802965

What am I doing wrong and how do I correct it??

 

[karipeters]

When you are faced with an ugly calculation such as the above, first do an approximation.

\(\displaystyle -.05 +1.3 - 8.3 + 31.15 + 4.9 = 29\)

Now one answer that you could give is "approximately 29." All those decimals are meaningless because they do not teach decimals in unicorn school.

However, if you believe that what is wanted is an EXACT answer, the approximation will at least prevent you from making a big mistake. You know the answer must be fairly close to 29.

With numbers so ugly, doing things step by step is a sensible idea, but keep your equation intact. An equation is a tool that helps you avoid mistakes. You engaged in several double additions by not keeping your equation intact.

\(\displaystyle f(x) = -0.047578125+1.28634375 - 8.291875+31.15+4.914\)

\(\displaystyle f(x) = 1.238765625 - 8.291875+31.15+4.914\)

\(\displaystyle f(x) = -7.053109375+31.15+4.914\)

\(\displaystyle f(x) = 24.096890625+4.914\)

\(\displaystyle f(x) = 29.010890625 \)

Do I guarantee that I made no errors in transcribing these numbers? No. Am I pretty sure I made no gross errors? Yes, I am because this answer agrees with the approximate answer found above.

Oh my goodness thank you!!! I followed off the above part to finish the second part...could you tell me if this part is correct or did I mess up somewhere?

 

[karipeters]

For the second half of this problem, this is what I came up with. Is this correct??

f(x) = - 0.001218x4 + 0.082326x3 – 1.3267x2 + 12.46x + 4.914
f(12)= - 0.001218(12)4 + 0.082326(12)3 – 1.3267(12)2 + 12.46(12) + 4.914
= - 0.001218(20736) + 0.082326(1728) – 1.3267(144) + 12.46(12) +4.914
= -25.256448 + 142.259328 – 191.0448 + 149.52 +4.914
= 117.00288 -191.0448 + 149.52 +4.914
= -74.016 + 149.52 + 4.914
= 75.504 + 4.914
= 80.418