1.quotient n.【数】商(the number resulting from the division of one number by another)

例：lf you divide 26 by 2,the quotient is 13.

2.raccoon n．浣熊

例：Raccoons are shy and active only at night.

3.racism n.种族歧视(racial prejudice or discrimination)；种族主义(a belief that race is the primary determinant of human traits and some races are superior to others)

词根记忆：rac(e)（种族）+ism（……主义）——种族主义

同根词：racist(n．种族主义者)

4.radiant a．辐射的：发光的(radiating rays or reflecting beams of light)；容光焕发的(marked by or expressive of love confidence, or happiness)

词根记忆：radi(光线，射线)+ant—发光的—容光焕发的

例：a radiant smile灿烂的笑容

同根词：radiation(n.发光，传播)；radiator(n．散热器)

5.radiate v.放射，辐射(to send out in or as if in rays)

词根记忆：radi(光线)+ate—发光，放热—放射，辐射

例：The national observatory has been observing x-rays radiated by compact stars for years.

派生词：radiation(n．放射；放射物；放射线)

6.radical a．激进的(extreme, drastic)；n.激进分子(a person who is radical)

词根记忆：radic(根)+aI—根本不讲道理的—激进的

例：a radical feminist激进的女权主义者

派生词：radically( ad.彻底地；激进地)

7.radioactive a．放射性的，有辐射能力的(of, caused by or exhibiting radioactivity)

词根记忆：radi(辑射：光线)+o+active(活跃的)—发射光活跃的—放射性的

例：Calcium carbonate shells contain radioactive material.

8.radiocarbon n．放射性碳

联想记忆：radio(无线的)+carbon(碳)—不经过实体传播的碳—放射性碳

例：Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.

9.radiusi n．半径(a line segment extending from the center of a circle or sphere to the circumference or bounding surface)

注意：diameter(n．直径)；circumference(n．圆周)

例：The radius of the circle is 0.5 meter.