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2025 National One Eighth mathematics Topic 9 Free

Number theory

Expressing $193$, $145$ and $157$ as sums of two squares of natural numbers · Sub-topic 1

ONE EIGHTH CONTEST 2025

Prempeh College - 62 points

Suhum SHTS - 37 points

Benkum SHS - 13 points


ONE EIGHTH CONTEST 2025

Mfantsipim School - 53 points

Anglican SHS, Kumasi - 37 points

Sogakope SHS - 24 points


ONE EIGHTH CONTEST 2025

Adisadel College - 82 points

St. Hubert Seminary SHS - 24 points

Serwaa Nyarko Girls' SHS - 24 points


ROUND 1

PREAMBLE

Express the given number as a sum of two squares of Natural Numbers

FIRST QUESTION

193

ANSWER: $7^{2}+12^{2}$


SECOND QUESTION

145

ANSWER: $1^{2}+12^{2}$ or $8^{2}+9^{2}$


THIRD QUESTION

157

ANSWER: $6^{2}+11^{2}$


PRACTICE QUESTIONS


1. Express 65 as a sum of two squares of natural numbers.

ANSWER: $1^2+8^2$ or $4^2+7^2$


SOLUTION

Subtract each square from 65 and check whether the result is a square:

$65-1^2=64=8^2$

$65-2^2=61$

$65-3^2=56$

$65-4^2=49=7^2$

$65-5^2=40$

$65=1^2+8^2=1+64$

$65=4^2+7^2=16+49$


2. Express 85 as a sum of two squares of natural numbers.

ANSWER: $2^2+9^2$ or $6^2+7^2$


SOLUTION

Subtract each square from 85 and check whether the result is a square:

$85-1^2=84$

$85-2^2=81=9^2$

$85-3^2=76$

$85-4^2=69$

$85-5^2=60$

$85-6^2=49=7^2$

$85=2^2+9^2=4+81$

$85=6^2+7^2=36+49$


3. Express 89 as a sum of two squares of natural numbers.

ANSWER: $5^2+8^2$


SOLUTION

Subtract each square from 89 and check whether the result is a square:

$89-1^2=88$

$89-2^2=85$

$89-3^2=80$

$89-4^2=73$

$89-5^2=64=8^2$

$89-6^2=53$

$89=5^2+8^2=25+64$


4. Express 113 as a sum of two squares of natural numbers.

ANSWER: $7^2+8^2$


SOLUTION

Subtract each square from 113 and check whether the result is a square:

$113-1^2=112$

$113-2^2=109$

$113-3^2=104$

$113-4^2=97$

$113-5^2=88$

$113-6^2=77$

$113-7^2=64=8^2$

$113=7^2+8^2=49+64$


5. Express 41 as a sum of two squares of natural numbers.

ANSWER: $4^2+5^2$


SOLUTION

Subtract each square from 41 and check whether the result is a square:

$41-1^2=40$

$41-2^2=37$

$41-3^2=32$

$41-4^2=25=5^2$

$41=4^2+5^2=16+25$


6. Express 97 as a sum of two squares of natural numbers.

ANSWER: $4^2+9^2$


SOLUTION

Subtract each square from 97 and check whether the result is a square:

$97-1^2=96$

$97-2^2=93$

$97-3^2=88$

$97-4^2=81=9^2$

$97-5^2=72$

$97-6^2=61$

$97=4^2+9^2=16+81$