﹙1﹚71×69=﹙70+1﹚×﹙70-1﹚=70²-1²=4900-1=4899;
﹙2﹚﹙x-4﹚﹙x+4﹚﹙x²+16﹚
=﹙x²-16﹚﹙x²+16﹚
=x^4-16²
=x^4-256
﹙3﹚﹙3m+2n﹚²-﹙2m+3n﹚²
=﹙3m+2n-2m-3n﹚﹙3m+2n+2m+3n﹚
=5﹙m-n﹚﹙m+n﹚
=5m²-5n²
﹙1﹚71×69=﹙70+1﹚×﹙70-1﹚=70²-1²=4900-1=4899;
﹙2﹚﹙x-4﹚﹙x+4﹚﹙x²+16﹚
=﹙x²-16﹚﹙x²+16﹚
=x^4-16²
=x^4-256
﹙3﹚﹙3m+2n﹚²-﹙2m+3n﹚²
=﹙3m+2n-2m-3n﹚﹙3m+2n+2m+3n﹚
=5﹙m-n﹚﹙m+n﹚
=5m²-5n²