Thread: checking my answer with another answer...

im having problem with this

(2+3i) (5-7i)
the answer the teacher got is
31+i

i got 31-34i

what did i do wrong?

Thanks,
candy

Originally Posted by Candy101

im having problem with this

(2+3i) (5-7i)
the answer the teacher got is
31+i

i got 31-34i

what did i do wrong?

Thanks,
candy

Since you didn't include your working it's impossible to know what you did wrong. However, you would be advised to note that -14i + 15i = i.

oh so sorry

first i multiple out
(2+3i) (5-7i)
and i got

10-14i-20i-21i^2

so i know that i^2 is -1 so ... 21i^2 became 21
giving me
10-14i-20i+21

i then combine -14i with -20i giving me -34i
then i added 10 with 21 giving me 31

thanks,
candy

Originally Posted by Candy101

oh so sorry

first i multiple out
(2+3i) (5-7i)
and i got

10-14i-20i-21i^2 ... there is your mistake. 3i(5) = 15i

...

omg i see it! gosh thanks!