Explanation:
length
a + b = 18cm
a = 18 - b
Area
a² + b² = 212cm²
(18-b)² + b² = 212
324 - 36b + b² + b² = 212
2b² - 36b + 112 = 0
b² - 18b + 56 = 0
b² - 4b - 14b + 56 = 0
b(b-4) -14(b - 4) = 0
(b-4) (b-14) = 0
b-4 = 0 OR. b-14 = 0
b = 4 cm b = 14 cm
so 4cm < 14cm
so , length of a side of the smaller square is 4cm .......
And , large square's = 14cm .....