My friend needed with this and i found the height through the theorem but can't figure out how to get the base of the overall triangle

You found CD from the Pythagorean theorem to be ...

... CD = √(5² -2²) = √21

Since triangle ADC ~ triangle ACB, the ratios of corresponding sides are the same:

... AC/AD = AB/AC

... AB = AC²/AD

... AB = 5²/2 = 12.5 . . . . . . . the base of the overall triangle

Then the area (A) is ...

... A = (1/2)bh

... A = (1/2)(12.5)(√21) ≈ 28.64 square units

As you see here, the altitude of a right triangle divides it into three similar triangles. From smallest to largest, they are ...

... ADC ~ CDB ~ ACB

You can figure this using AAA similarity, since the smallest and largest triangles listed above share an acute angle vertex (∠A). That, together with the right angle, means all angles are congruent. After that, then you know ∠ACD ≅ ∠CBD, so you can show the middle sized triangle is similar to the other two.

b. the decimal could be two-tenths.

step-by-step explanation:

its adding 5.5 each time

step-by-step explanation: