中二升中三數學唔識呀?help?

1.when a number is either corrected to 2 significant figures or 3 significant
figures, the results are the same.Write down the number.(列式)

the number is 127.3

When correcting to 2 sig. fig. , the number becomes 127

When correcting to 3 sig. fig. , the number also becomes 127

2.Suppose x(x+a)-10恆等(x-b)(x+c).Suggest a possible set of values of a,b and c.(列式)

x(x+a)-10=(x-b)(x+c)

x^2+ax-10=x^2+(c-b)x-bc

a=c-b-----1

bc=10----2

Let b =2 ,c=5 ,thus a=5-2=3

1.
780.4
When correcting to 2 sig. fig. , the number becomes 780
When correcting to 3 sig. fig. , the number also becomes 780
2.
x(x+a)-10=(x-b)(x+c)
x^2+ax-10=x^2+(c-b)x-bc
a=c-b-----1
bc=10----2
Let b =2 ,c=5 ,thus a=5-2=3