As shown in the figure, in the RT triangle ABC, ∠ C = 90, AC = 6cm, BC = 8cm, points E and f start from two points a and B at the same time and move to points c and B along the direction of AC and Ba respectively The velocity of point E is 2cm / s, and that of point F is 1cm / s. if one of the points reaches the position, both points stop moving (1) Q. after a few seconds, the area of the triangle AEF is 16 / 5 (2) After a few seconds, EF bisects the perimeter of the RT triangle (3) Is there a line EF that bisects the perimeter and area of rtabc at the same time? If so, calculate the length of AE. If not, explain the reason
1、 Make FG ⊥ AC through f point;
AC = 6, BC = 8, ∠ C = 90 ° and ab = 10;
The results show that Ag / AC = (ab-bf) / AB, that is, Ag = 0.6 (10-bf);
FG / BC = (ab-bf) / AB, that is, FG = 0.8 (10-bf);
S△AEF=AG*FG/2=0.24(10-BF)^2;(1)
When s △ AEF = 16 / 5, substitute (1) to get BF = 10-2 √ 30 / 3, or 10 + 2 √ 30 / 3 (rounding off);
Since the velocity of BG is 1cm / s, s △ AEF is 16 / 5 after (10-2 √ 30 / 3) seconds (about 6.35 seconds);
2、 Half of the circumference of RT △ ABC = (AB + AC + BC) / 2 = (10 + 6 + 8) / 2 = 12 > ab;
So point E is on the extension line of AC; it is also called FG ⊥ AC;
AE=2BF;
EG=AE-AG=2BF-0.6(10-BF)=2.6BF-6;
EF^2=EG^2+FG^2=(2.6BF-6)^2+(0.8(10-BF))^2;(2)
When EF = 12 (half of the circumference of RT △ ABC), substitute (2)
BF = (√ 809.6 + 22) / 7.4, about 6.818cm;
After 6.818 seconds, EF bisects the perimeter of RT △ ABC;
3、 RT △ ABC perimeter = 24; SRT △ ABC = 6 * 8 / 2 = 24;
Therefore, if EF bisects the cycle length, it also bisects the area;
At this time, AE = 2BF = (√ 809.6 + 22) / 3.7, about 12.636cm;